Component with reduced stress forces in the substrate

ABSTRACT

A component with a magnetic field sensor. The electronic component is located in a semiconductor substrate or on the surface of the semiconductor substrate and is surrounded at least partially, preferably largely, by a trench in the semiconductor substrate. The trench is filled with a filling material.

CROSS-REFERENCE TO RELATED APPLICATIONS

None.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a magnetic field sensor, wherein the magneticfield sensor is surrounded partially by a trench in a semiconductorsubstrate.

Brief Description of the Related Art

FIG. 3 shows a cross section of a possible embodiment of a lateral Hallsensor 300 which is implemented in CMOS technology on a siliconsubstrate 310 and which has a sensitivity to a vertical component of amagnetic field (along the z-axis). The functional layers of the Hallsensor 300 are located below a surface 315 of the silicon substrate 310in corresponding regions 320, 330 of the semiconductor substrate 310.The functional layers are limited by means of doping. The first layer320 in this embodiment is an n-type layer and the second layer 330 lyingon top is a p-type layer. The contact to the Hall sensor 300 and toother components in the silicon substrate 310 is effected in a furtherlayer structure on the substrate by means of metal conductor paths 340and 350. From FIG. 3 it can be seen that the metal conductor paths 340and 350 contact the doping regions via corresponding contact diffusions345 and 355.

The Hall sensor 300 can also be formed as an array with a plurality ofinterconnected Hall elements. Depending on the embodiment, the array caninclude lateral and vertical Hall elements which, are sensitive to thevertical and/or horizontal components of the magnetic field.

Other magnetic field sensors such as TMR, AMR, etc. can usually beattached on the surface 315 of the semiconductor substrate 310. Theteaching of this document encompasses also magnetic field sensors andother electronic components that have an integrated component on thesurface of a semiconductor substrate and in which the integratedcomponent extends or can extend into the semiconductor substrate 310(such as those implemented using CMOS technology).

It is known that the piezoresistive and piezo-Hall effect impairs theperformance of Hall sensors. The complex mechanical stress conditionsthat are caused during the packaging process or otherwise in thesemiconductor substrate 310 to or in which a Hall sensor 300 is attachedcan only be insufficiently determined. Their influence on the Hallelements can be compensated only conditionally and with considerableeffort. Further, the induced mechanical stress in the Hall element showsa strong dependence on environmental conditions such as, for example,temperature and relative humidity. Slow changes in the mechanical stressover the lifetime of the Hall sensor 300 and the other components causedby plastic deformations (in the composite body) can likewise be detectedonly insufficiently and can be only used to a limited extent for acompensation of these influences on the properties of the Hall sensor300.

Various methods are known in the art, which compensate for theinfluences on the sensor element of mechanical stress conditions in thesemiconductor substrate. For example, for offset reduction, theso-called “current spinning” method is used, also known as “currentswitching” method.

The spinning current method is known, in connection with lateral Hallsensors 300 for suppressing the offset of the sensor signal, from thebook “Rotary Switch and Current Monitor by Hall-Based Microsystems” byRalph Steiner Vanha, Publisher Physical Electronics Laboratory, SwissFederal Institute of Technology (ETH) Zurich, 1999, pages 39-53. Thespinning current method consists in continually, cyclically rotatingfurther by, for example, 90° the measurement and current direction ofthe Hall sensor 300 at a certain clock frequency, forming a sum over allmeasuring signals using a full rotation by 360° and thereby reducing theinfluence of offset voltages.

The long-term drift of the magnetic sensitivity of the Hall sensors isdiscussed in the publication “Compensation of the Piezo-Hall-Effect inIntegrated Hall Sensors on (100)-Si”, Udo Ausserlechner et al., IEEESensors Journal vol. 7, no. 11, November 2007, 1475-1482. The authorsfound that this long-term drift is caused by changes in the mechanicalstress formation in the semiconductor substrate by the packaging. Inthis publication, a system is disclosed which measures the stresscomponents in the semiconductor substrate and thus estimates thesensitivity drift. A correction can be made in the ascertained measuredvalues. The U.S. Pat. No. 7,980,138 also discloses this device. Thepatent protects a method for stress measurement on an IC by means of atleast two interconnected piezoresistive resistors.

From U.S. Pat. No. 5,600,074 (Marek et al.) a silicon semiconductorsubstrate for use in a force sensor is known. This patent shows trenchesarranged in parallel for the protection of electrical circuits frommechanical stress upon vertical loading of a semiconductor substrate.

The sensitivity drift of the Hall sensor 300, caused by changes in themechanical stress conditions after adjustment of the Hall sensor 300 canbe compensated with the system from the Ausserlechner publication.However, the mechanical stress sensors are themselves subject to anundesirable cross-dependence, such as, for example, from thetemperature, which in turn must be also compensated. It is also knownthat the mechanical stress measurement in a semiconductor substrate isvery complicated and requires chip space (“real estate”), which is nolonger available for other components or which increases the currentconsumption and the production costs of the integrated circuit. Aninaccuracy of the measured values also results from the fact that themechanical stresses in the semiconductor substrate are measured inlocations other than the mechanical stresses that act directly in theregion of the Hall sensors. The additional stress measurements alsorequire an increased effort of processing of the measuring signals,which in turn is related to a higher circuit complexity.

To address these disadvantages, the Japanese patent application no. JPH09-97895 and the Japanese patent application no. 2004-235328 describe amagnetic field sensor on or in a semiconductor substrate, wherein themagnetic field sensor is at least partially surrounded by a trench in asemiconductor substrate. Thus, the mechanical stress components in thesemiconductor substrate are largely avoided in the region of thesurface.

The manufacturing process described in these Japanese patentapplications is such that this trench can be filled partially orcompletely during the subsequent packaging process of the magnetic fieldsensor, i.e. during the insert molding (encapsulation) of the componentswith the casting compound. This results in a rigid mechanical connectionbetween the trench walls, through which mechanical stresses can betransferred from one side to the other. Therefore, the desired stressreduction is strongly reduced or completely canceled in the region ofthe sensor element. (Depending on the type of filler used, it is evenpossible to increase the mechanical stress state in the sensor region)

When the trench is filled only partially with the encapsulationmaterial, cavities are formed which can be filled with water when thecomponent is exposed to moisture. A sudden rise in temperature, such asthat which occurs, for example, during the soldering of a packagedcomponent, then leads to the bursting of the outer shell (popcorneffect) and thus to the destruction of the component.

Various other prior art documents are known. For example, German PatentApplication No DE 10 2011 002 580 A1 shows a semiconductor substratewith a surface and magnetic field sensor with trenches that surround atleast part of the magnetic field sensor. The trenches are filled with anoxide. The oxide is rigid and is not able to absorb stresses in thesemiconductor substrate.

German Patent Application No DE 20 2005 014 157 and US PatentApplication publication No. US 200/70290682 also disclose semiconductorsubstrates with trenches. Neither of these applications teaches that thetrench is filled with a resilient material that it is able to absorbstresses in the substrate.

SUMMARY OF THE INVENTION

To address these and other disadvantages of the state of the art, thetrench in the semiconductor substrate is filled with a suitablematerial, which is resilient and will be hereinafter referred to asbuffer material. The filler can no longer intrude into the trench duringinsert molding. The buffer material is resilient and thus is able toabsorb the stress, which arises in the composite body during manufactureand does not pass them through to the sensor.

Further, an additional layer of a buffer material can be applied to thesemiconductor substrate to absorb mechanical stresses acting between thesilicon or sensor surface (island) and the casting compound.

In a further exemplary embodiment, the trench and the sensor elementsare covered with a cap to prevent the intrusion of the filler into thetrench during the encapsulation process. The cap is adhesively bondedsuitably on the silicon substrate, and typically can have a recess orcavity in the region of the trench and of the sensor element.

In one aspect both of the methods can be combined, i.e. the cap can alsobe adhesively bonded over a filled trench with/without buffer layer.

With the aid of this structure, it is no longer required to provideadditional sensors for the measurement of the mechanical stress and asignal processing processor for the evaluation of the compensatingeffects. The silicon area (real estate) for these additional componentsis not utilized and the power consumption is reduced.

With regard to manufacturing technology, in one embodiment the trench ispreferably produced by means of a laser removal. Alternatively, theremoval can also be effected by means of a suitable physical dry etchingprocess (reactive ion etching (RIE), deep reactive ion etching (Boschprocess, DRIE), ion beam cutting), or by wet-chemical etching using KOHor EDP for example.

In one aspect, the magnetic field sensor is largely surrounded by thetrench; thereby forming an island in the semiconductor substrate withthe magnetic field sensor. A connection between a signal processingprocessor and the magnetic field sensor is provided on a connectingbridge between the island and the other part of the semiconductorsubstrate by conducting paths running on it or highly conductivediffusions in the silicon substrate.

In order to achieve a sufficient isolation of the mechanical stress, thetrench has a depth amounting to, for example, at least one twentieth ofthe diagonal of the island on the surface or 5 μm. In a differentaspect, the trench can penetrate fully through the silicon substrate.The width of the trench amounts to less than 100 μm, so that not toomuch silicon area is utilized. The trench is subsequently filled with afilling material (buffer material).

The magnetic field sensor can be a Hall sensor or other sensor which issensitive to mechanical stresses. Moreover, together with the Hallsensor, the island can contain several further components which have across-sensitivity to mechanical stresses and are required for signalprocessing of the magnetic field sensor/sensors, such as, for example,analog to digital converters or voltage and current sources forsupplying the sensor.

Still other aspects, features, and advantages of the present inventionare readily apparent from the following detailed description, simply byillustrating a preferable embodiments and implementations. The presentinvention is also capable of other and different embodiments and itsseveral details can be modified in various obvious respects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and descriptions are to be regarded asillustrative in nature, and not as restrictive. Additional objects andadvantages of the invention will be set forth in part in the descriptionwhich follows and in part will be obvious from the description, or maybe learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionand the accompanying drawings, in which:

FIG. 1 shows a side view of the component.

FIG. 1B shows a plan view of the component.

FIG. 1C shows the side view with filled trench.

FIG. 1D shows the side view of a component with a lid.

FIGS. 2A-2B and FIGS. 2D-2N and FIG. 2P show several constructioncomponents with differently arranged connecting bridges.

FIG. 3 shows a lateral Hall sensor according to the state of the art.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows a side view of a component 10 according to one aspect ofthis invention. A magnetic field sensor 30 is introduced or integratedinto a semiconductor substrate 20 or arranged on a surface 25 of thesemiconductor substrate 20.

The magnetic field sensor 30 is surrounded at least partially by atrench 40. As can be seen in FIG. 1b , the trench 40 in this aspect ofthe disclosure surrounds the electronic component 30 largely, but notcompletely, forming a kind of “island” 35 in the semiconductor substrate20.

A connecting bridge 50 passes between the island portion of the surface25 and the other part of the semiconductor substrate 20. Metal conductorpaths 60 extend via the connecting bridge 50 which connect the magneticfield sensor 30 on the island 35 with further metal conductor paths onthe remaining part of the surface 25. A Hall sensor requires, forexample, at least four lines 60 for the four connectors or electronicconnections. The electrical connections can be implemented also by meansof suitable diffusions on the connecting bridge instead of metalconductor paths.

The trench 40 has a depth t_(t), which should be at least 5 μm, or onetwentieth of the diagonal H_(d) of the island 35 on the surface 25. Thetrench 40 can also penetrate the semiconductor substrate 20 fully. Thetrench 40 around the island 35 results in the magnetic field sensor 30being largely isolated from stress forces in the semiconductor substrate20. The magnetic field sensor 30 on the island 35 is thus not influencedby the stress forces in the semiconductor substrate 20.

As can be seen from FIGS. 2A-2B and FIGS. 2C-2N and FIG. 2P, theconnecting bridge 60 is not required to run centrally on one side of theisland in the trench 40. The connecting bridge 50 can also be arrangedon the side, as can be seen from FIG. 2B. Two connecting bridges 50 canbe present likewise (see FIG. 2D). In some other embodiments, the trench40 is not required to fully surround the island 35 to achieve thedesired isolation of the stress forces or to prevent the spreading ofthe same. FIG. 2E-2H show aspects of the structure, for example, inwhich the trench 40 does not fully surround the island 35. Although themechanical isolation in the aspects according to 2E-H is not as strongas in other aspects, the manufacture of such trenches 40 can be achievedmore cost-effectively, and the island 35 is connected to the remainingsemiconductor substrate 20 in a mechanically more robust fashion.

FIG. 2I-2M show other embodiments of the trench 40, wherein in FIG. 2Mthe trench 40 is formed without a connecting bridge 50. The contactingof the electronic component can be established in this case by bondingconnections for example. Furthermore, it is possible that the magneticfield sensor 30 can contain not only one single electronic component onits surface 25, but also have additional components 70. FIG. 2L shows adifferent form of the trench 40 with a further component 70. FIG. 2Pshows a possible embodiment with an island 35 on the edge of thesemiconductor substrate 20 and FIG. 2N shows a possible embodiment withan island in a corner of the semiconductor substrate 20.

The trench 40 is obtained by a conventional etching process, for exampleby laser removal or other physical or wet-chemical etching. As otheretching processes dry etching processes (reactive ion etching—RIE, deepreactive ion etching—Bosch process, DRIE and ion beam cutting), orwet-chemical etching by means of KOH or EDP can be considered. Themagnetic field sensor 30 and the other components are manufactured byconventional production steps.

The trench 40 in FIG. 1C is optionally lined partially on its innersurface (passivated) with one or several components for protectionagainst environmental influences. As a lining layer 42, a nitride suchas Si₃N₄ or a polyimide is preferably used. The trench 40 is completelyfilled, with or without lining, wherein the filling of the trench canalso be effected with several layers of different buffer materials. Thebuffer material/the buffer materials 45 has/have typically a smallerelasticity and/or bulk modulus than the substrate. As the buffermaterial, preferably a polymer is used, for example an elastomer such asa silicon compound or other suitable material, which can absorb themechanical stresses that occur in the filled trench. However, the buffermaterial can also be an epoxy resin. The filling of the trench 40 allowsa further encapsulation of the component, wherein no, or only smallmechanical stresses are transferred from the substrate to the island viathe filling material 45.

A further buffer layer 46 can be applied to the surface 25 of thesemiconductor substrate and the filled trench 40. This buffer layerabsorbs the mechanical stresses acting from the sealing compound on thesurface of the island. The buffer layer typically covers at least theisland as well as the trench and thus covers the entire Si surface onlypartially. In one aspect, the buffer layer consists of the same materialwith which the trenches are filled. Alternatively, the buffer layer 46from a plastic foil can be applied by adhesive bonding on the surface25. (FIG. 1C shows a trench 40 with encapsulation layer 42 and bufferfilling material 45 and buffer layer 46.)

FIG. 1D shows a component with a cap 80 which is attached over theisland by means of an adhesive layer 81. The cap 80 encloses an airvolume 82 in its cavity. The cap protects the trench against theintrusion of material during the encapsulation process and against theintrusion of moisture and the formation of water reservoirs in thetrench. Alternatively, the cap 80 can also be applied to a componentwith a filled trench with/without buffer layer over the island surface.The cap 80 is typically manufactured of a non-magnetic material. When anon-magnetic and electroconductive material is used, such as copper, forexample, the sensor element is additionally shielded fromelectromagnetic radiation.

Moreover, in addition to the magnetic field sensor 30, the component 10can also have several magnetic field sensors and include circuitrycomponents that have a cross-sensitivity to mechanical stresses and arerequired for the signal processing of the magnetic field sensor/sensors,such as, for example, analog to digital converter, or voltage andcurrent sources for supplying the sensor.

The foregoing description of the preferred embodiment of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and modifications and variations are possible in lightof the above teachings or may be acquired from practice of theinvention. The embodiment was chosen and described in order to explainthe principles of the invention and its practical application to enableone skilled in the art to utilize the invention in various embodimentsas are suited to the particular use contemplated. It is intended thatthe scope of the invention be defined by the claims appended hereto, andtheir equivalents. The entirety of each of the aforementioned documentsis incorporated by reference herein.

1. A component comprising: a semiconductor substrate with a surface; amagnetic field sensor; and a trench filled with a filling material inthe semiconductor substrate, said trench surrounding the magnetic fieldsensor at least partially, wherein the filling material is a buffermaterial for absorbing mechanical stresses.
 2. The component accordingto claim 1, wherein the surface has a buffer layer.
 3. The componentaccording to claim 1, wherein the trench and the magnetic field sensorare covered with a cap.
 4. The component according to claim 1, whereinthe trench surrounds the magnetic field sensor largely, in order to forman island, and further has a connecting bridge.
 5. The componentaccording to claim 4, further comprising conductor paths, diffusions orbonding connections, which contact the electronic connections of themagnetic field sensor and are guided over the connecting bridge.
 6. Thecomponent according to claim 1, wherein the magnetic field sensor isintegrated in the semiconductor substrate.
 7. The component according toclaim 1, wherein the magnetic field sensor is a Hall sensor.
 8. Thecomponent according to claim 1, wherein the trench has a depth which isat least 5 μm or one twentieth of the diagonal of the magnetic fieldsensor.
 9. The component according to claim 1, wherein the trenchpenetrates the semiconductor substrate fully.
 10. The componentaccording to claim 1, wherein the width of the trench is less than 100μm.
 11. The component according to claim 1, wherein the filling materialis a polymer or polyimide.
 12. The component according to claim 1,wherein the surface of the trench has an encapsulation layer.
 13. Thecomponent according to claim 12, wherein the encapsulation layer is anitride.
 14. The component according to claim 1, wherein the trench isproduced by laser removal.
 15. A construction element with a componentcomprising a semiconductor substrate with a surface; a magnetic fieldsensor; and a trench filled with a filling material in the semiconductorsubstrate, said trench surrounding the magnetic field sensor at leastpartially, comprising a further component that is surrounded at leastpartially by the trench, wherein the filling material is a buffermaterial for absorbing mechanical stresses.
 16. The construction elementaccording to claim 15, wherein the further component is a circuitrycomponent for controlling the magnetic field sensor.
 17. Theconstruction element according to claim 15, wherein the furthercomponent is a circuitry component for capturing the data from themagnetic field sensor.